Various devices (e.g., smartphones, tablet PCs, etc.) and technologies requiring Machine-to-Machine (M2M) communications and high data throughputs continue to appear and tend to be popularized. And, a data amount necessary to be processed on a cellular network is increasing very fast. In order to meet the fast increasing data processing requirement amount, technologies (e.g., carrier aggregation technology, cognitive radio technology, etc.) for using more frequency bands efficiently and technologies (e.g., multi-antenna technology, multi-base station cooperation technology, etc.) for increasing data capacity transmitted within a limited frequency are developed. And, a communication environment is evolved in a direction of increasing density of nodes accessible by a nearby user equipment. A node means a fixed point capable of transmitting/receiving a radio signal to/from a user equipment by being equipped with at least one antenna. A communication system equipped with nodes of high density can provide a user equipment with a communication service of high performance by cooperation between the nodes.
According to the multi-node cooperative communication scheme of performing communication with a user equipment using the same time-frequency resource at a plurality of nodes, since each node operates as an independent base station, such a scheme has performance much better than that of an existing communication scheme of performing communication with a user equipment without mutual cooperation.
A multi-node system performs a cooperative communication using a plurality of nodes that operate as a base station (or, access point), an antenna, an antenna group, a radio remote header (RRH) and a radio remote unit (RRU). Unlike the existing center concentrated antenna system having antennas concentrated on a base station, a plurality of the nodes in the multi-node system are located in a manner of being spaced apart from each other over a predetermined interval. A plurality of the nodes can be operated by at least one base station or a base station controller configured to control an operation of each node or schedule data to be transmitted/received through each node. And, each of the nodes is connected to the base station or the base station controller configured to operate the corresponding node through a cable or a dedicated line.
Such a multi-node system may be regarded as a sort of MIMO (multiple input multiple output) system in that distributed nodes can communicate with single or multiple users by transmitting/receiving different streams simultaneously. Yet, since the multi-node system transmits a signal using the nodes distributed to various locations, a transmitting area supposed to be covered by each antenna is reduced in comparison with antennas provided to an existing centralized antenna system. Hence, compared to the existing system capable of implementing the MIMO technology in the centralized antenna system, the multi-node system can reduce a transmit power required for each antenna to transmit a signal. Moreover, since a transmitting distance between an antenna and a user equipment is reduced, a pathloss is reduced and a fast transmission of data is enabled. Hence, transmission capacity and power efficiency of a cellular system can be raised and a communication performance of a relatively uniform quality can be met irrespective of a location of a user equipment within a cell. In the multi-node system, since base station(s) or base station controller(s) connected to a plurality of nodes cooperates for data transmission/reception, a signal loss generated from a transmitting process is reduced. In case that nodes located by being spaced apart from each other over a predetermined distance perform cooperative communication with a user equipment, correlation and interference between antennas are reduced. Hence, according to the multi-node cooperative communication scheme, it is able to obtain a high SINR (signal to interference-plus-noise ratio).
Owing to the advantages of the multi-node system mentioned in the above description, in order to extend a service coverage and improve channel capacity and SINR as well as reduce a base station establishment cost and a maintenance cost of a backhaul network in a next generation mobile communication system, the multi-node system is used together with or substituted with the existing centralized antenna system, thereby emerging as a new base of a cellular communication.